经过对象直接增删该查

@SpringBootTest

class SpringbootDemo2MybatisApplicationTests {

    @Autowired

    private UserDao userDao;

    @Test

    public void testFind(){

        List<User> userList = userDao.findAll();

        System.out.println(userList);

    }

    @Test

    public void testSelect01(){

        List<User> userList = userDao.selectList(null);

        System.out.println(userList);

    }

    /**

 * 业务: 查询id=11的用户信息   主键...

 */

    @Test

    public void testSelect02(){

        User user = userDao.selectById(11);

        System.out.println(user);

    }

    /**

 * 业务: 查询name属性为"小乔"的数据

 * sql:  select * from user where name="小乔";

 * 对象的方式  >  sql方式

 */

    @Test

    public void testSelect03(){

        //条件构造器

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.eq("name", "小乔");

        List<User> userList = userDao.selectList(queryWrapper);

        System.out.println(userList);

    }

    /**

 * 业务: 查询name属性为"小乔"的数据 而且 age >=18岁

 * sql:  select * from user where name="小乔" and age>=18;

 *

 * 大于   >  gt| 小于 <  lt   |

 * 大于等于  >= ge  |  小于等于 le

 */

    @Test

    public void testSelect04(){

        //条件构造器

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.eq("name", "小乔")

                    .ge("age", 18);

        List<User> userList = userDao.selectList(queryWrapper);

        System.out.println(userList);

    }

    /**

 * 业务: 查询name中包含 "精"的用户,而且sex为女

 * 业务: 查询name中包含 以精结尾的数据,而且sex为女

 * sql:  select * from user where name like "%精%" and sex="女";

 */

    @Test

    public void testSelect05(){

        //条件构造器

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.likeLeft("name", "精")

                    .eq("sex", "女");

        List<User> userList = userDao.selectList(queryWrapper);

        System.out.println(userList);

    }

    /**

 * 需求: 查询user表中的数据 要求按照年龄降序排列,若是年龄相同按照id降序排列

 */

    @Test

    public void testSelect06(){

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.orderByDesc("age","id");

        List<User> userList = userDao.selectList(queryWrapper);

        System.out.println(userList);

    }

    /**

 * 需求: 查询name属性为null的数据.

 * where name is null

 */

    @Test

    public void testSelect07(){

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.isNull("name");

        List<User> userList = userDao.selectList(queryWrapper);

        System.out.println(userList);

    }

    /**

 * 查询name="小乔" age=17 性别=女的用户

 * 若是传递的是对象.会根据对象中不为null的属性充当where条件.

 */

    @Test

    public void testSelect08(){

        User user = new User();

        user.setName("小乔").setAge(17).setSex("女");

        QueryWrapper<User> queryWrapper = new QueryWrapper<>(user);

        List<User> userList = userDao.selectList(queryWrapper);

        System.out.println(userList);

    }

    /**

 * 查询id=1,3,5,10数据.

 * sql: select * from user where id in (1,3,5,10)

 */

    @Test

    public void testSelect09(){

        //转化时,注意使用对象的类型

        Integer[] ids = {1,3,5,10};

        List<Integer> idList = Arrays.asList(ids);

        List<User> userList = userDao.selectBatchIds(idList);

        System.out.println(userList);

    }

    @Test

    public void testInsert(){

        User user = new User();

        user.setName("特朗普").setAge(70).setSex("男");

        userDao.insert(user);

    }

    /**

 * 删除name=null的数据,或者name="特朗普"

 */

    @Test

    public void testDelete(){

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.isNull("name")

                    .or()

                    .eq("name", "特朗普");

        userDao.delete(queryWrapper);

    }

    /**

 * 案例1: 将id=1的数据的年龄改成8000岁.

 * sql1:  update user set age=8000 where id=1;

 * 案例2: 要求将name="黑熊精" age=5500.

 * sql2:  update user set age=5500 where name="黑熊精";

 */

    @Test

    public void testUpdate(){

        User user = new User();

        user.setId(1);    //主键充当where条件

        user.setAge(8000);

        userDao.updateById(user);

        //参数说明  1.实体对象  封装set条件的值

        //           2.更新条件构造器

        User temp = new User();

        temp.setAge(5500);

        UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();

        updateWrapper.eq("name", "黑熊精");

        userDao.update(temp,updateWrapper);

    }

}

2.pojo层实现实现实现实现实现
@Data
@TableName  //("user")      //1.将对象与表 进行一对一关联
public class User implements Serializable {
    @TableId(type = IdType.AUTO)    //主键的信息  设定自增
    private Integer Id;
    //@TableField("name")     //若是字段名称与属性的名称一致(包含驼峰规则),能够省略不写
    private String name;
    private Integer age;
    private String sex;
}

mapper层层层层层层层层层层层层层层层层层层层层层层层层层层层
public interface UserDao extends BaseMapper<User> {

//查询user表的全部的记录
@Select("select * from user")
List<User> findAll();

}
//mapperscan包名写在mapper层
@SpringBootApplication
@MapperScan("com.jt.mapper")
public class SpringbootDemo3WebApplication {

public static void main(String[] args) {

SpringApplication.run(SpringbootDemo3WebApplication.class, args);

}

}